From WO 2003/099619 A2, a reversible seat belt tensioner is known wherein the drive shaft transmitting the rotational movement of the electric motor to the belt shaft is coupled to the electric motor via a crown gear unit and is coupled to the drive wheel via a worm gear unit.
A disadvantage in this embodiment is that the arrangement of the components with respect to each other cannot be freely chosen, as the gear wheels of the gear units deflect the rotational movement by 90 degrees each, and, therefore, the rotational axes of the meshing rotating components have to be arranged at an angle of 90 degrees with respect to each other. It has further turned out that the noises developing in the crown gear unit and in the worm gear unit during the seat belt tensioning, in particular for vehicles of the higher quality class, are no longer tolerated by the vehicle manufacturers.